WASHINGTON — The Supreme Court on Thursday unanimously ruled that a Thai student who in 2013 won a copyright case involving imported textbooks should have another chance to persuade a lower court that the textbook’s publisher should pay his legal fees.

The usual rule in American civil litigation is that each side pays its own lawyers regardless of who wins. But the Copyright Act allows judges to “award a reasonable attorney’s fee to the prevailing party.”

Federal appeals courts have applied different standards in deciding when fee awards in copyright cases are warranted. The judge in the student’s case, in New York, awarded him nothing, relying on a decision from the federal appeals court there that focused on whether the losing side’s position had been “objectively reasonable.”

The publisher easily met that standard, the judge said, as it had won a $600,000 judgment against the student, won an appeal in 2011 and lost in the Supreme Court by a 6-to-3 vote in 2013.

Justice Elena Kagan, writing for the court, said whether the losing side’s position was objectively reasonable should play a major role in the analysis. But she said the United States Court of Appeals for the Second Circuit, in New York, and the district courts it supervises, may have placed nearly dispositive weight on that one factor.

Justice Kagan said other considerations — including motivation, deterrence and compensation — must also play a role in the analysis. But she appeared to suggest that the student, Supap Kirtsaeng, was unlikely to prevail under the correct standard.

This was Mr. Kirtsaeng’s second trip to the Supreme Court. In 2013, he prevailed, with six justices agreeing that he had been entitled to help finance his American education by selling textbooks imported from Thailand. Since publishers charged different prices for essentially the same books in the two markets, Justice Kagan wrote on Thursday, there was “a ripe opportunity for arbitrage.”

The 2013 ruling, which clarified an ambiguous phrase in the Copyright Act, said imported copyrighted goods were subject to the same rules as goods bought in the United States: Owners of particular copies can do what they like with them.

In the new case, Kirtsaeng v. John Wiley & Sons, No. 15-375, Mr. Kirtsaeng sought more than $2 million in legal fees from John Wiley & Sons, the publisher that had sued him.

Even as the Supreme Court handed Mr. Kirtsaeng a modest victory on Thursday, it rejected his main argument. He had said courts should give special consideration to whether the lawsuit in question had helped clarify a difficult and important legal issue. Awarding legal fees to the winning side, he said, would encourage such cases to be litigated.

“Kirtsaeng’s proposal would not produce any sure benefits,” Justice Kagan wrote. “Fee awards are a double-edged sword: They increase the reward for a victory — but also enhance the penalty for a defeat.”

In a footnote, Justice Kagan considered how Mr. Kirtsaeng himself might have calculated whether to proceed in the earlier case, concluding that the decision probably turned on his appetite for risk. Among his possible reactions, she wrote, were “six of one, half a dozen of the other,” “depends if I’m feeling lucky that day” and “the higher the stakes, the greater the rush.”

A version of this article appears in print on , Section B, Page 2 of the New York edition with the headline: Justices Allow the Victor in a Copyright Case to Seek Legal Fees. Order Reprints | Today’s Paper | Subscribe